1. Field of the Invention
The present invention relates to an interferometric modulator and a display unit with the interferometric modulator, and more particularly to an interferometric modulator that is suitably employed for a reflection type display unit.
2. Description of the Related Art
Generally, the reflection type display unit employs the ambient light, and is particularly useful for the mobile purposes.
Currently, the typical reflection type display units are employed in a TN (Twisted Nematic) mode or an STN (Super-Twisted Nematic) mode using the birefringence or optical rotatory power of the liquid crystal.
However, in these display modes, it is required to use a polarizing plate, in which an optical loss by the polarizing plate is as large as about 60%, so that the display is darker.
On the other hand, a guest-host method in which dichroic dye is added to liquid crystal and a transmitting/scattering method represented by a dynamic scattering mode have been proposed as the liquid crystal display method without using the polarizing plate. However, these display methods have lower contrast and are impractical. An electrophoresis method of color particles in a solution, a dichroic rotary particle (twisted ball) method, and a toner display method have been proposed as the display method using other than the liquid crystal, but have not been put to practical use because of the problems with the driving voltage, contrast, response speed, stability and life.
In recent years, a new display method without using the polarizing plate, called an iMod™ method, in which interference of incident light is modulated by driving of a micro machine (Micro Electro Mechanical System: MEMS), has been disclosed in U.S. Pat. No. 5,835,255 and Japanese National Phase Publication No. 2000-500245. This method is a reflection type display system for modulating interference of an ambient light by changing electrostatically the spacing of a cavity (interferometric modulator cavity) having two walls, one being a reflector (metal) and the other being an induction absorber (metallic absorber sandwiched between dielectrics). In this system, a monochrome display with red (R), green (G) or blue (B) and a black display can be switched. That is, light of a wavelength corresponding to the optical distance is reflected to the observer in a state where the reflector and the induction absorber are separated apart by a specified optical distance, based on a Fabry-Pérot interference principle, and displayed in monochrome. Also, incindet light in a visible radiation region is prevented (absorbed) from being reflected by adjusting this optical distance, and displayed in black.
This system has an advantage that CF is unnecessary because of monochrome display by interference. Also, it has advantages such as a high contract ratio, a low consumption power, and a high speed response of MEMS. Furthermore, this system makes it possible to omit TFT by effectively using a hysteresis of MEMS.
However, since the bright display with the iMoD™ method is “monochrome display” using optical interference, there is a great dependence on the angle of incidence, causing a chromatic aberration depending on the viewing angle. To reduce or remove this chromatic aberration, an auxiliary front lighting and an optical compensation mechanism are required. Moreover, a color display has a laser-like color tone with a specific wavelength as the center. On the other hand, the white display is limited by a bandwidth (e.g., FWHM) of interference reflection of each color, because each pixel of RGB is realized by additive color mixture, whereby the Y value of the white display is difficult to increase. This is less preferable in the respect of application to the electronic books specific to the white/black display. Also, it is necessary to fabricate a pixel having a different structure for each display color. Moreover, with this iMoD™ method, a binary display of bright and darkness is made, and a half tone display is only possible by using a spatial dithering (area gradation method) based on the pulse width modulation, resulting in a large load.